diurne

Diurne is an adjective and sometimes a noun in English that denotes relation to daytime or the daily cycle. The form is mostly encountered in historical, technical, or French-influenced usage, with the more common English adjective being "diurnal." In practice, diurne may appear in older scientific texts, botanical writings, or law where French borrowings survive.

In science and daily language, diurne describes phenomena or behaviors that occur during daylight hours or over a 24-hour cycle. In astronomy, diurnal refers to phenomena tied to Earth's rotation, such as diurnal motion of the stars and the Sun's apparent path across the sky. In biology, diurnal organisms are active during the day, contrasting with nocturnal species. In meteorology or climatology, diurnal variation describes daily fluctuations in temperature, humidity, or atmospheric pressure.

Etymology: from Latin diurnus meaning daily, via Old French diurne; English uses "diurnal" as the more common form today, while "diurne" is chiefly found in older texts and some scientific or legal contexts.